A mold for continuous casting is a mold formed by using copper plates. In a mold for continuous casting, a space corresponding to the thickness and the width of a strand to be cast is formed by copper plates, where the space allows passage therethrough in the vertical direction. In addition, in order to cool and solidify molten steel poured in a mold, the outer surface (the cooled surface) of each copper plate is cooled. Molten steel poured from the upper side of a mold for continuous casting as above into a mold is cooled and solidified from a portion in contact with the inner surface (the molten-steel surface) of each copper plate, and pulled out downward in succession while being solidified.
Cooling of a mold is effected by water cooling of the outer surfaces of the copper plates. For example, as illustrated in FIG. 19, a large number of water-introducing grooves 2c are formed on the outer surface (cooled surface) 2b of a copper plate 2 which constitutes a mold. On the other hand, the outer surface 2b of the copper plate 2 suppresses deformation of the copper plate 2 which may be caused by thermal stress occurring in the copper plate 2, and is fixed with bolts 8 at multiple positions to a lid made of copper and called a back plate 4, which is a strength member for retaining the inner dimensions and shape of the mold. Thus, the opening portions of the water-introducing grooves 2c are covered by the back plate 4, and water-flow channels in which cooling water flows w are formed.
In addition, a hole 2d is formed in the copper plate 2 so as to evade the water-introducing grooves 2c and penetrate from the back plate side 4b through the back plate 4 into the copper plate 2. A temperature detection unit 6 which detects the mold temperature is inserted into the hole 2d. Conventionally, a sheathed thermocouple or the like has been used as the temperature detection unit 6. The detection result of the temperature detection unit 6 is provided for monitoring the situation in the mold, and is used, for example, for detection of a trouble such as a breakout. In the breakout, a shell as an outer-surface solidified portion of molten steel breaks and the molten steel leaks out. In addition, it is said that the temperature distribution occurring in the copper plate 2 reflects, for example, the flow of the molten steel in the mold. The detection result of the temperature detection unit 6 is also used for monitoring of judgment as to whether or not the quality of the slab is good.
The temperature detection unit 6 is inserted into the hole 2d from the back plate 4 side, and installed by fixing a fixing portion 6a to the back plate 4 as illustrated in FIG. 19. The fixing portion 6a is, for example, a screw member, and the temperature detection unit 6 can be fixed to the back plate 4 by screwing the fixing portion 6a into a thread groove formed in the vicinity of the opening of the hole 2d in the back plate 4. At this time, the temperature detection unit 6 is arranged in such a manner that the tip end of the thermocouple as a temperature detection point is located on a molten-steel surface 2a side of the tip ends (the bottoms of the grooves) of the water-introducing grooves 2c in the thickness direction of the copper plate 2. Because a temperature gradient, which is approximately a linear interpolation between the cooling water temperature and the temperature of the molten-steel surface 2a, is formed between the tip ends of the water-introducing grooves 2c and the molten-steel surface 2a, the temperature of the molten-steel surface 2a can be estimated by locating the temperature detection point of the temperature detection unit 6 between the tip ends of the water-introducing grooves 2c and the molten-steel surface 2a. 